The present invention relates generally to a retracting sootblower wallbox sealing assembly for an opening in the wall of a large scale boiler. More specifically, the present invention is directed to a sootblower wallbox constructed to absorb noise emanating from the nozzle of a retractable sootblower lance.
To optimize the thermal efficiency of a heat exchanger or boiler, it is necessary to periodically remove deposits such as soot, slag and flyash from the interior heat exchanging surfaces of the boiler. Typically, a number of cleaning lances, also known as sootblowers, are mounted exteriorly of the boiler and are inserted periodically into the boiler through ports located in the boiler wall. Positioned on the forward end of the lances are one or more cleaning nozzles. The nozzles discharge a pressurized cleaning medium, such as air, steam or other solutions. The effects of the high pressure cleaning medium are such that deposits of soot, slag and flyash are dislodged from the internal structures of the boiler.
Conventional wallbox assemblies serve a number of purposes. One purpose being that of a support structure for the previously mentioned cleaning lances. During cleaning, numerous combustion by-products escape to the exterior of the boiler between the cleaning lance and the walls of the cleaning port. For this reason, another purpose of a wallbox assembly is to retain combustion by-products within the boiler.
Wallbox assemblies designed to retard the escape of combustion by-products generally incorporate two chambers, a sealing air chamber and an aspirating air chamber. Both chambers provide air to the wallbox at a pressure greater than the internal operating pressure of the boiler. When the sootblower lance is dispensed through the wallbox for cleaning, positive pressure sealing air is provided to the wallbox assembly. Once the cleaning lance is removed, aspirating air is directed interiorly of the heat exchanger through an annular array of ports. The orientation of the aspirating ports, along with the increased pressure of the aspirating air, restricts the flow of combustion by-products from the cleaning port during normal operation of the boiler.
While being effective for their intended functions, modern sootblower systems tend to exhibit high noise emissions. In addition to normal operational noise of the boiler, noise is generated as the cleaning medium exits the lance nozzle during a cleaning cycle. The cleaning noise escaping from the wallbox assembly can generate extensive sound pressure outside the boiler.
In view of the foregoing, a principle object of the present invention is to provide a wallbox assembly which effectively limits the noise emissions associated with sootblower operation.
Another object of the present invention is to provide a wallbox assembly of a simple construction which thereby facilitates fabrication, service and maintenance.
A further object of the present invention is to provide a wallbox assembly capable of reducing noise emissions while also preventing the emission of combustion by-products from the assembly.
In the present invention, a sootblower wallbox assembly is provided with a number of sound absorbing reverberant annular chambers which surround the sootblower lance. The chambers are positioned coaxially and are bounded by baffle rings in close fit relation with the outside diameter of the lance. In order to achieve the desired sound attenuation characteristics, each chamber has a specific frequency range where it achieves its most significant noise reduction.
Since the reverberant chambers reduce noise by negative reinforcement, each chamber has its best noise absorption centered about a frequency having a wavelength four times the length of the chamber. From this it can be noted that a plurality of chambers having various lengths must be provided in order to obtain noise reduction throughout the audible frequency range. In designing a wallbox assembly having a minimum number of resonating chambers, care must be taken in choosing chamber lengths so that each chamber will significantly increases the overall effective attenuation of the assembly.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.